The drinking water, industrial wastewater or drainage needs its effective purification due to being contaminated with heavy metal ions, nasty smelling and tasting materials, organotoxic materials, etc.
If heavy metal ions are intaken in the human body through food chain of an ecosystem in spite of small amount, they are not eliminated from the body but continuously accumulated in the body, which causes harmful effects in many ways to the physiological process of the body.
The conventional methods for removal of heavy metal ions in the rivers, underground water or wastewater have been proceeded by using the chemical precipitation, ion exchange resin, separation membrane, etc. However, in case of using the chemical precipitation method, an abundant sludge produced after purification with precipitation method becomes a secondary contaminant and the heavy metal ions in low concentrations can not be easily removed by this method. Also, in case of the removal using ion exchange resin or separation membrane, it is difficult and expensive to treat the polluted water containing a lot of heavy metal contaminant.
Recently, the development of biological techniques using living organisms for the removal of heavy metal ions as an alternative method of solving the problems has been actively researched as a rapidly growing area of interest. The adsorption of heavy metal ions using living organism has been mainly researched with microorganisms even though it is possible to use the polymers originated from plants and animals. This is based on the facts that natural materials originated from the certain microorganisms have a capability that adsorbs and removes the heavy metal ions. The most actively employed microorganism in research is algae. Because algae have the advantage that it is the most abundant in nature. Also, in case of commercializing it can be easily and inexpensively produced in large scale due to being able to be grown with the sunlight as an energy resource without organic carbon source.
The generally used adsorbent using algae for removal of heavy metal ions is mainly prepared by immobilizing whole cells of algae to the supporter such as silica gel. The method in U.S. Pat. No. 5,055,402 is a typical example of extracting or removing the heavy metal ions by immobilizing whole cells of microorganisms, especially algae, to the supporter. The immobilizing step in the patent is essential to easily separate the whole cells of algae from the purification water in removal of heavy metal ions. Because it is difficult to apply the method using filtering or centrifuging to the industrial process even though solid algae can be separated from liquid purification water by filtering or centrifuging in the laboratory.
On the other hand, immobilizing step for preparing the adsorbents causes subsequent difficulties as well as extra expense for immobilizing the composition for water purification using microorganisms. That is, it can happen that the adsorption capability of algae is decreased as a result of immobilizing and that algae is desorbed from the immobilizing supporter in the middle of the water purification process. Also, the price of cells of algae is not reasonable because algae are not yet commercially available for use of water purification, furthermore they are not suitable for use of water purification because cells of algae emit a chromatic component and spread unique odor in case of contacting with water.
It is known for a composition of the cell membrane of algae to take main part in showing characteristics that algae adsorb heavy metal ions. One of compositions composing of cell membrane of algae is alginic acid. Also, it is known that alginic acid has 240,000 of molecular weight and water adsorption capacity of 200 to 300 fold greater than its weight. Even though it chemically belongs to carbohydrate, alginic acid is capable of adsorbing heavy metal cations by using the method such as ion exchange because it has anion as a natural polymer containing carboxylic group. Korean Patent Laid-Open No. 95-17756 discloses that alginate salt removes heavy metal ions using its characteristics of heavy metal ions adsorption. Also, the invention of the patent application discloses a system comprising of a reaction container to stir a mixture of a purification composition and a solution containing heavy metal ions, and a filtering container to separate the metal ions by filtering due to not being considered the immobilizing process. However, the method using such a separated process is too expensive and not practical to apply to the water purification process on a large scale. Also, it can show difficulty in the separation process because sodium alginate increases the viscosity of treating water by absorbing the treating water in the water purification process due to its high absorption property.
The materials with irresolvability not being removed by microorganisms such as algae can be removed by using the adsorption apparatus containing an activated carbon in the water purification process. Also; in some cases, an activated carbon powder is added to the mixture in the middle of the chemical precipitation purification process.
In order to treat heavy metals polluted water, there are a highly effective purification method of treating with microorganisms, a physicochemical purification method, and an activated carbon purification method of not treating with microorganisms. Due to manufacturing diverse materials in the chemical industry, the wastewater from a factory is various. Accordingly, the compositions and concentrations of wastewater are diverse. There are so many cases capable of utilizing the characteristics of the adsorption method using an activated carbon in chemical engineering because there are a variety of materials not capable of being biologically decomposed or organotoxic materials.
Conventionally, the two-step process has been used in order to remove heavy metal ions and organotoxic materials in treating water. However, the removal of heavy metal ions was not well performed. Also, the two-step process itself is highly expensive as well as ineffective. Accordingly, it is demanding the development of a water purification composition to remove all of them effectively.
It has been conventionally used the method using a reverse osmotic pressure membrane as a composition for water purification in the area of purifier to remove polluted materials of drinking water. However, there is disadvantage that the reverse osmotic pressure membrane removes up to the mineral components such as calcium, potassium, magnesium, sodium, etc. which is useful to the body as well as all of heavy metal ions, organic materials, etc. It is because the reverse osmotic pressure membrane does not have selectivity for those components. Also, the reservoir is easily contaminated by bacteria due to low rate of purification, which causes a high expense because it need a special apparatus.
Recently, to overcome such disadvantages of the method using the reverse osmotic pressure membrane, it is widely being developed the water purifier which can be used in a manner of directly connecting to a water pipe. As a water purification apparatus for water purifier, there are cartridge containing hollow filament membrane and activated carbon (Korean Pat. Laid-Open Nos. 92-11300 and 95-16813), cartridge containing ion exchange resin and activated carbon (Korean Patent Laid-Open No. 94-13575), etc.
In case of using the cartridge containing hollow filament membrane and activated carbon, there is a problem that the removal capability of heavy metal ions is very low. Also, in case of using the cartridge with ion exchange resin and activated carbon connected to a water purifier, there are problems of high expense for purification and no selectivity for metal ions.
Accordingly, the present inventors have developed alginate gel for water purification to effectively, selectively remove heavy metal ions and organotoxic materials in a water purifier as well as heavy metal polluted water system.